Sunrise, the startup behind the acclaimed email service and iOS calendar app of the same name, has raised a $2.2 million seed round led by Resolute and NextView Ventures, with participation from well-known angels like Dave Morin, Loic Le Meur and Hunter Walk.

Sunrise was founded as a bootstrapped startup by New York-based Pierre Valade and Jeremy Le Van, who left jobs at Foursquare to launch a daily email service that augmented your personal calendar with information from your social networks (think ‘Rapportive for calendars’). This was followed in February this year by the launch of the iOS app, which we described as “powerful, beautiful” and “supremely useful.”

Valade tells us that the funding will be used to continue to “build the best calendar app.” In addition to further development of the iOS version (including iCloud support), Android and Windows apps are on the roadmap – and not just on mobile, a desktop version is planned too. This seemed a little odd when Sunrise is so well-suited to a mobile screen, but Valade says that most agenda planning and admin tends to take place on the desktop, so he wants Sunrise to be there whenever a user needs their calendar.

To fuel these developments, Sunrise will soon have doubled its staff headcount from three at the time of the app’s initial launch, to six.

The iOS app now boasts 200,000 registered users and Valade says that 20% of early adopters continue to use it on at least a weekly basis – a retention rate that he says he is happy with. Still, it’s not like he doesn’t have competition to worry about. Tempo AI’s Tempo and Flexbits’ FantastiCal are both solid competitors with their own fair share of hype.

Martin Bryant Editor-in-Chief at The Next Web. You can find him on Twitter, subscribe to him on Facebook, circle him on Google+ and visit his personal site. He's based in Manchester, UK and has a thing for quirky American music and Japanese video games.